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The Single UNIX &reg; Specification, Version 2<br>
Copyright &copy; 1997 The Open Group

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<h4>NAME</h4><blockquote>
t_sndv - send data or expedited data, from one or more
non-contiguous buffers, on a connection
</blockquote><h4>SYNOPSIS</h4><blockquote>
<pre><code>

#include &lt;<a href="xti.h.html">xti.h</a>&gt;

int t_sndv(
    int fd,
    const struct t_iovec *iov,
    unsigned it iovcount,
    int flags)
</code>
</pre>
</blockquote><h4>DESCRIPTION</h4><blockquote>
<pre>
<P><table  bordercolor=#000000 border=1 align=center><tr valign=top><th align=center><b>Parameters</b>
<th align=center><b>Before call</b>
<th align=center><b>After call</b>
<tr valign=top><td align=left>fd
<td align=center>x
<td align=center>/
<tr valign=top><td align=left>iovec
<td align=center>x
<td align=center>/
<tr valign=top><td align=left>iovcount
<td align=center>x
<td align=center>/
<tr valign=top><td align=left>iov[0].iov_base
<td align=center>x(x)
<td align=center>=(=)
<tr valign=top><td align=left>iov[0].iov_len
<td align=center>x
<td align=center>=
<tr valign=top><td align=left>   . . . .
<tr valign=top><td align=left>iov[iovcount-1].iov_base
<td align=center>x(x)
<td align=center>=(=)
<tr valign=top><td align=left>iov[iovcount-1].iov_len
<td align=center>x
<td align=center>=
<tr valign=top><td align=left>flags
<td align=center>x
<td align=center>/
</table>
</pre>
<p>
This function is used to send either normal or expedited
data.  The argument 
<I>fd</I>
identifies the local transport
endpoint over which data should be sent, 
<I>iov</I>
points to an
array of buffer address/buffer length pairs.  
<i>t_sndv()</i>
sends data contained in buffers 
<I>iov[0]</I>,
<I>iov[1]</I>,
through 
<I>iov[iovcount-1]</I>.
<I>iovcount</I>
contains the number of
non-contiguous data buffers which is limited to T_IOV_MAX
(an implementation-defined value of at least 16).  If the
limit is exceeded, the function fails with [TBADDATA].
<p>
<dl><dt><b>Note:</b>
<dd>The limit on the total number of bytes available
in all buffers passed (that is:
<I>iov(0).iov_len + . . + iov(iovcount-1).iov_len</I>)
may be constrained by
implementation limits. If no other constraint applies,
it will be limited by [INT_MAX]. In practice, the
availability of memory to an application is likely to
impose a lower limit on the amount of data that can be
sent or received using scatter/gather functions.
</dl>
<p>
The argument 
<I>flags</I>
specifies any optional flags described below:
<dl compact>

<dt>T_EXPEDITED<dd><br>
If set in
<I>flags</I>,
the data will be sent as
expedited data and will be subject to the
interpretations of the transport provider.

<dt>T_MORE<dd><br>
If set in 
<I>flags</I>,
this indicates to the
transport provider that the transport
service data unit (TSDU) (or expedited
transport service data unit - ETSDU) is
being sent through multiple 
<i>t_sndv()</i>
calls.
Each 
<i>t_sndv()</i>
with the T_MORE flag set
indicates that another 
<i>t_sndv()</i>
(or 
<i><a href="t_snd.html">t_snd()</a></i>)
will follow with more data for the current TSDU (or ETSDU).

The end of the TSDU (or ETSDU) is identified
by a 
<i>t_sndv()</i>
call with the T_MORE flag not
set.  Use of T_MORE enables a user to break
up large logical data units without losing
the boundaries of those units at the other
end of the connection.  The flag implies
nothing about how the data is packaged for
transfer below the transport interface.  If
the transport provider does not support the
concept of a TSDU as indicated in the 
<I>info</I>
argument on return from 
<i><a href="t_open.html">t_open()</a></i>
or
<i><a href="t_getinfo.html">t_getinfo()</a></i>,
the T_MORE flag is not
meaningful and will be ignored if set.

The sending of a zero-length fragment of a
TSDU or ETSDU is only permitted where this
is used to indicate the end of a TSDU or
ETSDU, that is, when the T_MORE flag is not
set. Some transport providers also forbid
zero-length TSDUs and ETSDUs.  See 
<xref href=istpi></xref>
for a fuller explanation.

</dl>
If set in <I>flags</I>, requests that the provider transmit all data
that it has accumulated but not sent.  The request is a local action
on the provider and does not affect any similarly named protocol
flag (for example, the TCP PUSH flag). This effect of setting
this flag is protocol-dependent, and it may be ignored entirely
by transport providers which do not support the use of this feature. 
<p>
<dl><dt><b>Note:</b>
<dd>The communications provider is free to collect
data in a send buffer until it accumulates a sufficient
amount for transmission.
</dl>
<p>
By default, 
<i>t_sndv()</i>
operates in synchronous mode and may
wait if flow control restrictions prevent the data from
being accepted by the local transport provider at the time
the call is made.  However, if O_NONBLOCK is set (via
<i><a href="t_open.html">t_open()</a></i>
or 
<i><a href="fcntl.html">fcntl()</a></i>),
<i>t_sndv()</i>
executes in asynchronous
mode, and will fail immediately if there are flow control
restrictions.  The process can arrange to be informed when
the flow control restrictions are cleared via either
<i><a href="t_look.html">t_look()</a></i>
or the EM interface.
<p>
On successful completion, 
<i>t_sndv()</i>
returns the number of
bytes accepted by the transport provider.  Normally this will
equal the total number of bytes to be sent, that is,
<pre>
<code>
<I>(iov[0].iov_len +  .. . . + iov[iovcount-1].iov_len)</I>
</code>
</pre>
<p>
However, the
interface is constrained to send at most INT_MAX bytes in a single
send.  When 
<i>t_sndv()</i>
has submitted INT_MAX (or lower constrained value, see the note above)
bytes to the provider for a single call, this value
is returned to the user.  
However, if
O_NONBLOCK is set or the function is interrupted by a signal, it
is possible that only part of the data has actually been
accepted by the communications provider.  In this case, 
<i>t_sndv()</i>
returns a value that is less than the value of nbytes.  If
<i>t_sndv()</i>
is interrupted by a signal before it could transfer data
to the communications provider, it returns -1 with 
<I>t_errno</I>
set to [TSYSERR] and 
<I>errno</I>
set to [EINTR].
<p>
If the number of bytes of data in the 
<I>iov</I>
array is zero and sending
of zero octets is not supported by the underlying transport
service, 
<i>t_sndv()</i>
returns -1 with 
<I>t_errno</I>
set to [TBADDATA].
<p>
The size of each TSDU or ETSDU must not exceed the limits of
the transport provider as specified by the current values in
the TSDU or ETSDU fields in the 
<I>info</I>
argument returned by
<i><a href="t_getinfo.html">t_getinfo()</a></i>.
<p>
The error [TLOOK] is returned for asynchronous events. It is required
only for an incoming disconnect event but may be returned for
other events.
</blockquote><h4>VALID STATES</h4><blockquote>
T_DATAXFER, T_INREL
</blockquote><h4>ERRORS</h4><blockquote>
On failure, 
<I>t_errno</I>
is set to one of the following:
<dl compact>

<dt>[TBADDATA]<dd>Illegal amount of data:
<ul>

<li>
A single send was attempted specifying
a TSDU (ETSDU) or fragment TSDU (ETSDU)
greater than that specified by the
current values of the TSDU or ETSDU
fields in the 
<I>info</I>
argument.

<li>
A send of a zero byte TSDU (ETSDU) or
zero byte fragment of a TSDU (ETSDU) is
not supported by the provider.

<li>
Multiple sends were attempted resulting
in a TSDU (ETSDU) larger than that
specified by the current value of the
TSDU or ETSDU fields in the 
<I>info</I>
argument - the ability of an XTI
implementation to detect such an error
case is implementation-dependent (see
CAVEATS, below).

<li>
<I>iovcount</I>
is greater than T_IOV_MAX.

</ul>

<dt>[TBADF]<dd>The specified file descriptor does not refer to a transport endpoint.

<dt>[TBADFLAG]<dd>An invalid flag was specified.

<dt>[TFLOW]<dd>O_NONBLOCK was set, but the flow control
mechanism prevented the transport provider
from accepting any data at this time.

<dt>[TLOOK]<dd>An asynchronous event has occurred on this
transport endpoint.

<dt>[TNOTSUPPORT]<dd>This function is not supported by the
underlying transport provider.

<dt>[TOUTSTATE]<dd>The communications endpoint referenced by
<I>fd</I>
is not in one of the states in which a call to this function is valid.

<dt>[TPROTO]<dd>This error indicates that a communication
problem has been detected between XTI and
the transport provider for which there is no
other suitable XTI error
<I>(t_errno)</I>.

<dt>[TSYSERR]<dd>A system error has occurred during execution
of this function.

</dl>
</blockquote><h4>RETURN VALUES</h4><blockquote>
On successful completion, 
<i>t_sndv()</i>
returns the number of
bytes accepted by the transport provider.  Otherwise, -1 is
returned on failure and 
<I>t_errno</I>
is set to indicate the error.
<p>
<dl><dt><b>Notes:</b>
<dd><ol>
<p>
<li>
In synchronous mode, if more than INT_MAX bytes of data
are passed in the 
<I>iov</I>
array, only the first INT_MAX bytes will be
passed to the provider.
<p>
<li>
If the number of bytes accepted by the communications
provider is less than the number of bytes requested, this may
either indicate that O_NONBLOCK is set and the communications
provider is blocked due to flow control, or that O_NONBLOCK is
clear and the function was interrupted by a signal.
<p>
</ol>
</dl>
</blockquote><h4>SEE ALSO</h4><blockquote>
<i><a href="t_getinfo.html">t_getinfo()</a></i>,
<i><a href="t_open.html">t_open()</a></i>,
<i><a href="t_rcvv.html">t_rcvv()</a></i>,
<i><a href="t_rcv.html">t_rcv()</a></i>,
<i><a href="t_snd.html">t_snd()</a></i>.
</blockquote><h4>CAVEATS</h4><blockquote>
It is important to remember that the transport provider
treats all users of a transport endpoint as a single user.
Therefore if several processes issue concurrent 
<i>t_sndv()</i>
or 
<i><a href="t_snd.html">t_snd()</a></i>
calls, then the different data may be intermixed.
<p>
Multiple sends which exceed the maximum TSDU or ETSDU size
may not be discovered by XTI.  In this case an
implementation-dependent error will result (generated by the
transport provider), perhaps on a subsequent XTI call.  This
error may take the form of a connection abort, a [TSYSERR],
a [TBADDATA] or a [TPROTO] error.
<p>
If multiple sends which exceed the maximum TSDU or ETSDU
size are detected by XTI, 
<i>t_sndv()</i>
fails with [TBADDATA].
</blockquote><hr size=2 noshade>
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UNIX &reg; is a registered Trademark of The Open Group.<br>
Copyright &copy; 1997 The Open Group
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